Erosion and Sediment Pollution Control Program Manual.pdf

INTRODUCTION (Adapted from the Delaware Erosion and Sediment Control Handbook)
PA DEP
Plant & Soil Sciences elibrary
Figure I.1 Raindrop Impact
363-2134-008 / March 31, 2012 / Page xv
“What is the harm if a little
mud washes into the
stream?” “Erosion takes
place all the time naturally,
so what’s the big deal?”
“Do you know how much
money these erosion
control BMPs are costing
me?” These are questions
that earthmovers ask us all
the time. They are
legitimate questions that
deserve an answer. First,
let’s look at the natural
process of erosion, then
how it is affected by
earthmoving projects, and
finally how that affects both
the environment and all of
us as residents and tax
payers.
Soil erosion is the process by which the land’s surface is worn away by the action of wind, water, ice
and gravity. Natural or geologic erosion has been occurring at a relatively slow rate since the earth was
formed, and is a tremendous factor in the creation of the earth as we know it today. The rolling hills of
the Allegheny Plateau, the steep slopes of the Valley and Ridge Province, and the relatively low profile
of the Coastal Plain are all results of the geologic erosion and sedimentation process in Pennsylvania.
Except for some cases of shoreline and stream channel erosion, natural erosion occurs at a slow rate
and is an important factor in maintaining an ecological balance.
Water-generated erosion is the most severe type of erosion, especially in developing areas. It is this
type of erosion that is the focus of this manual. Water-generated erosion occurs as a result of the
impact of rain droplets on unprotected soil surfaces and is due to frictional forces on soil particles as
those rain droplets combine and move across the surface of the land. The force due to impact of
raindrops is primarily vertical and tends to detach soil particles, while the force of flowing water is
primarily horizontal and acts to move detached particles from one place to another.
TYPES OF EROSION
Water-generated erosion can be broken down into the
following types:
Raindrop Erosion is the initial effect of a rainstorm
upon the soil. Raindrop impact dislodges soil
particles and splashes them into the air (See
Figure I.1). These detached particles are then
vulnerable to the following types of erosion.
Sheet Erosion is caused by the shallow flow of
water over the land’s surface before it concentrates.
Although seldom the detaching agent, it can
transport soil particles detached by raindrop impact.
Sheet erosion has been identified as a major cause of soil loss on agricultural fields. Although there